Why would someone leave the scene of a traffic death? Psychologists have few answers.

Over the past eight days, three people died and another was injured in three hit-and-run accidents in the Baltimore region. Police are still seeking the drivers in all three incidents.

On Wednesday, Bishop Heather Elizabeth Cook was indicted on charges of automobile manslaughter, driving under the influence, texting while driving, and leaving the scene of the accident that killed bicyclist Thomas Palermo just days after Christmas.

What leads someone to flee an accident where another person might have suffered harm?

Data shows fleeing an accident is not uncommon, but there's little research on the behavior. Psychologists and others struggle to explain the hit-and-run phenomenon.

Every year, there are an average of 24 deaths in Maryland and about 1,600 across the country involving hit-and-run drivers who strike someone on foot, riding a bike or in another car — numbers that have remained fairly steady over three decades, according to a Sun analysis of federal data.

Those who study human behavior say the drivers likely experience a flood of emotions including fear, shame and guilt, which overwhelm their sense of self-control. That can be made worse by alcohol, a factor in about 30 percent of traffic fatalities nationally.

"Rational decision-making is clearly difficult in an intoxicated state, particularly as blood-alcohol levels increase," said Carlo DiClemente, a psychology professor at University of Maryland, Baltimore County who studies addictive behavior. "Fear and escape motivations kick in and, without good executive functioning, make flight more probable."

People also are strongly motivated to avoid the consequences, said E. Scott Geller, psychology professor in the Center for Applied Behavior Systems at Virginia Tech. But such avoidance actions are usually moderated by a person's upbringing and culture.

People generally own up to their mistakes if they have been positively recognized for good behavior and telling the truth, he said. Conversely, those always severely punished for their behavior would be less likely to take responsibility.

But also shaping someone's character, and their response, is positive recognition for bad behavior. As an example, Geller cited cyclist Lance Armstrong, who won multiple Tour de France titles while using performance-enhancing drugs. (He has since been stripped of his medals.)

With his history of cheating, winning and not owning up, Geller said, it "wasn't surprising" that police in Aspen, Colo., recently accused Armstrong of crashing into parked cars on Dec. 28 and leaving his girlfriend to take the blame. Police cited Armstrong with failing to report an accident and speeding after his girlfriend, who was initially charged, acknowledged lying for him. Charges against her were dropped.

"How many hit-and-run drivers return later to own up?" Geller said. "I hope quite a few, after their values or character strengths of integrity and/courage take over."

Officials for the AAA Foundation for Traffic Safety said there is little research on hit-and-run drivers, though it remains a consistent problem.

The most recent incident in the Baltimore region came early Wednesday in Elkridge, where a 33-year-old Baltimore woman walking on U.S. 1 died after being struck by two cars, one of which fled the scene, according to police. Two other fatal hit-and-runs occurred on the Baltimore-Washington Parkway last weekend.

The majority of hit-and-runs occur on weekends, when more people are out walking, and at night, when it's harder to see, said Jurek Grabowski, AAA's research director and an injury epidemiologist.

He said the group emphasizes that drivers, cyclists and pedestrians all need to be more aware of others on the road and need to make sure they can be seen. That means using reflective gear for walkers and cyclists, and not drinking or using cellphones for those behind the wheel. The group also advocates strong laws, as well as advertising and enforcing those laws.

It's illegal to drive with a blood-alcohol concentration above 0.08 percent in any state. And as of 2014, 12 states and Washington, D.C., have banned hand-held cellphones while driving; and 41 states and Washington, D.C., have banned texting while driving, according to federal transportation officials. Maryland has enacted both bans.

No research can show how often drivers who fled accidents were under the influence of alcohol or distracted by technology.

From 1982 to 2012, an average of about 4 percent of traffic deaths in Maryland and nationally involved a hit-and-run driver, according to a Sun analysis of data from the National Highway Traffic Safety Administration.

In 2012, the most recent data available, drivers in Maryland fled the scene of 26 of the 479 total traffic deaths. Some of the crashes involved more than one death. Nationally, drivers left the scene of 1,487 of 32,074 traffic deaths.

More study is needed to understand how to combat the problem, said Frank Farley, a psychologist in Temple University's department of psychological, organizational and leadership studies and a former president of the American Psychological Association.

It may be tough to research because many hit-and-run drivers are never caught. And even if they were found and studied, there likely isn't one "ironclad personality profile proven in science," said Farley, who studies the risk-taking personality.

He said there are likely several personality types who would flee a car crash.

The first is the risk-taker, who is self-confident and energetic, and feels in control of fate. They drink more and are more likely to get into an accident, and would rather take the risk of running than face the consequences of staying.

Another type has little impulse control, he said. Fear, adrenaline and the "fight or flight" instinct kicks in and they act before they think. They might be most likely to return once they start thinking clearly.

Cook returned to the scene of Palermo's death about 30 minutes after the accident, while investigators were still there, authorities said.

A third type has "guilty knowledge," Farley said. They are doing something wrong, such as drinking or driving without a valid driver's license, or are with someone they aren't supposed to be. They also might be a police officer or a person in a leadership position, he said.

Celebrities such as Armstrong are likely averse to the publicity, he said. In fact, that's what his girlfriend told the Aspen police.

Still others may believe the crash is not their fault, so they leave rather than be — to their thinking — unfairly punished. And lastly, Farley said, some may have just had a bad upbringing and lack morals and empathy for their victims.

"There are likely many different aspects to a perpetrator's behavior," Farley said. "It's always a recipe, and there are several ingredients to a recipe. … In psychology we're never able to find one single cause of any behavior."